In a burner of solid, liquid or gaseous fuel it is of known importance to sense the presence of flame to monitor and verify burner operation. It is also important to verify correct combustion within the burner to control the emission of pollutant combustion products into the atmosphere.
A prior art methodology for detecting the presence of flame from combustion in burners is to use a photo resistor, typically of cadmium sulphide, to act as a light detector that responds to the light generated by the flame. A drawback of this methodology is that a photo resistor cannot accurately distinguish between sources of light, and can therefore give a false positive based on external light sources or even the glow of material heated by the burner. To minimize false positives the photo resistor can be located in the burner at positions that tend not to receive external light, such as the barrel of the burner, but these locations are exposed to the heat of combustion and requires a design that can withstand such extreme heat.